Apparatus and method for accurate detection of locomotive fuel injection pump solenoid closure

ABSTRACT

The invention relates to a system and method for detecting a closing of a solenoid. The system includes a capacity charge circuit electrically coupled to the solenoid. The capacity charge circuit conditions the current flow through the solenoid to increase the current in response to the closing of the solenoid. The invention also relates to a system and method that includes detecting a current through the solenoid and determining a current slope characteristic. The current slope characteristic is a function of the current and time. The method also includes conditioning an electrical characteristic of the solenoid such that the conditioning is in response to a current slope parameter. The current slope parameter defines a change in the current after removal of an electrical charge to the solenoid.

CROSS REFERENCE TO RELATED APPLICATIONS

The invention of the present application claims priority based on U.S.Provisional Application Ser. No. 60/506,555 filed on Sep. 26, 2003.

FIELD OF THE INVENTION

The invention relates generally to control of a fuel injection systemequipped with a fuel injection solenoid. In particular, the inventionrelates to an apparatus and method for controlling a fuel pump solenoidby detecting a closure of the solenoid.

BACKGROUND OF THE INVENTION

In engine systems, the accurate detection of fuel pump solenoid closureor closing point detection for each of the cylinders of the engine isdesirable to provide accurate timing of injection of fuel and control ofcombustion, emissions, smooth regulation of engine speed, and fuelefficiency. Prior art system and methods for detecting fuel injectionsolenoid closure involve detecting the change of slope of the solenoidcurrent within a window, as the current is reduced from peak pull-incurrent, to hold current. However, prior art systems are susceptible tovariations due to cable lengths between engine control unit and theengine cylinder solenoids, aging, ambient conditions, fuel pumps, andengine speed. Moreover, the location and the characteristic signature ofsuch a detection scheme may vary as a function of pump, impedance ofelectronics/cabling/solenoid, power supply voltage, engine speed,hydraulic fuel pressure, cam location, aging, and ambient conditions.These variations reduce the reliability and accuracy of conventionalmethods of closing point detection.

Detecting solenoid closure in a in a fuel injection system is desirablefor determining any required compensation in timing of fuel injection.The timing of fuel injection is a critical variable to control in orderto achieve operational goals such as combustion quality, fuel efficiencyand reduced emissions. Any inaccuracies in closing point detectionimpact these important goals. An appropriate algorithm with consistentdetection and accuracy helps achieve these goals.

Therefore, there is a need for an improved method of detection ofclosing point and minimizing the susceptibility of closing pointdetection due to variations that change the characteristics of currentwaveform. The present invention provides an improved method of closingpoint detection by regulating the slope from peak current to the timewhen the closing point is detected.

SUMMARY OF THE INVENTION

These and other problems are solved by one of the following features:(i) the signature characteristic of the current being controlled byregulating current slope in response to capacitive charge circuit; (ii)the closing point detection time window used for closing point detectionbeing a function of power supply voltage, and (iii) the time windowbeing adaptively varied to account for drifts, pump and solenoidvariations, ambient condition changes, and aging.

In one aspect, the invention relates to a system for detecting a closingof a solenoid. The system includes a capacity charge circuitelectrically coupled to the solenoid. The capacity charge circuitconditions the current flow through the solenoid to increase the currentin response to the closing of the solenoid.

In another aspect, the invention relates to a method for detecting aclosing of a solenoid. The method comprises conditioning the currentthrough the solenoid such that the current increases in response to theclosing of the solenoid.

In another aspect, the invention relates to a system for detecting aclosing point of a fuel injection pump solenoid associated with acylinder of a locomotive diesel engine. The system includes a solenoiddriver circuit for providing a current and a voltage to a winding of thesolenoid. The solenoid has a low side driver and a high side driver. Thesystem also includes a sensor for detecting the current through thewinding of the solenoid. A capacitive charge circuit is included formodifying the voltage and the current as a function of a capacitivecharge value. The system also includes a processor configured withcomputer instructions for determining the capacitive charge value. Theprocessor is electrically coupled to the capacitive charge circuit andprovides the capacitive charge to the capacitive charge circuit. Thesystem also includes a detector for detecting a change in a slope of thecurrent as a function of time. The change of slope changes from adecrease in current over time to an increase in current over time inresponse to the closing of the solenoid.

In yet another aspect, the invention relates to a system for detecting aclosing of a solenoid that includes a capacity charge circuitelectrically coupled to the solenoid. The capacitive charge circuitconditions a current through the solenoid in response to a current slopeparameter. The current slope parameter defines a change in the currentafter removal of an electrical charge to the solenoid.

In another aspect, the invention relates to a method for detecting aclosing of a solenoid. The method includes detecting a current throughthe solenoid and determining a current slope characteristic. The currentslope characteristic is a function of the current and time. The methodalso includes conditioning an electrical characteristic of the solenoidsuch that the conditioning is in response to a current slope parameter.The current slope parameter defines a change in the current afterremoval of an electrical charge to the solenoid.

In yet another aspect, the invention relates to a system for detecting aclosing of a solenoid. The system includes a current detectorelectrically coupled to the solenoid for detecting a current through thesolenoid. A processor determines a current slope characteristic whereinthe current slope characteristic is a function of the detected currentand time. The system also includes a capacity charge circuitelectrically coupled to the solenoid for conditioning the currentthrough the solenoid. The conditioning provides a change in the currentslope characteristic after removal of an electrical charge responsive toa current slope parameter.

In another aspect, the invention relates to a method for detecting theclosing point of a fuel injection pump solenoid associated with acylinder of a locomotive diesel engine. The method includes specifying adetection time period. The method also includes conditioning anelectrical characteristic applied to the solenoid by applying acapacitive charge characteristic to the solenoid. The conditioningchanges the current as a function of time. The method also includesdetecting a current through the solenoid and determining a currentslope. The current slope is the incremental change in the current inrespect to time. The method further includes detecting a change in thecurrent slope from a negative current slope to a positive current slopeand generating a signal in response to detecting the change in theslope.

In yet another aspect, the invention relates to a method for detecting aclosing of a solenoid that includes determining a closing point windowfor detection of the closing of the solenoid as a function of solenoidpower supply voltage.

In another aspect, the invention relates to a system for detecting aclosing point of a fuel injection pump solenoid associated with acylinder of a locomotive diesel engine. The system includes a solenoiddriver circuit providing a current and a voltage to a winding of thesolenoid. A sensor detects the current through the winding of thesolenoid. The system also includes a processor that is configured withcomputer instructions that specify a closing point window as a functionof solenoid power supply voltage. The processor also detects a change inthe current as a function of time during the closing point window.

In yet another aspect, the invention relates to a method for operating afuel injection system of a locomotive diesel engine that includesspecifying a closing point detection value for a cylinder of the dieselengine in response to a failure to detect the closing of the solenoid.When a speed and a timing of the diesel engine at the time of specifyingis comparable to a speed and timing of the diesel engine of thepreviously detected closing point detection values, the specifiedclosing point detection value is a function of an exponentially weightedaverage of previously detected closing point detection values. When thespeed and the timing of the diesel engine at the time of the specifyingvaries from a speed and a timing of the diesel engine associated with apreviously detected closing of the solenoid, the specified closing pointdetection value is a function of an average of generallycontemporaneously determined closing point values.

In another aspect, the invention relates to a system for operating afuel injection system of a locomotive diesel engine. The system includesa solenoid driver circuit that provides a current and a voltage to awinding of the solenoid. A sensor detects the current through thewinding of the solenoid. A memory stores the detected closing pointdetection values and a speed and a timing associated with the detectedclosing point values. The system also includes a processor that isconfigured with computer instructions. The computer instructions specifya closing point detection value for a cylinder of the diesel engine inresponse to a failure to detect the closing of the solenoid. Thespecified closing point detection value is a function of anexponentially weighted average of previously detected closing pointdetection values stored in the memory when a speed and a timing of thediesel engine at the time of specifying is comparable to a speed and atiming of the diesel engine of the previously detected closing pointdetection values. The specified closing point detection value is afunction of an average of generally contemporaneously determined closingpoint values as stored in the memory when the speed and the timing ofthe diesel engine at the time of the specifying varies a predeterminedamount from a speed and a timing of the diesel engine associated with apreviously detected closing of the solenoid.

Other aspects and features of the present invention will be in partapparent and in part pointed out hereinafter when the followingdescription is read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating components of one embodiment a solenoidcontrol system.

FIG. 2 is a chart illustrating solenoid current as a function of timeand timing lines associated with the electrical powering of the solenoidaffecting the solenoid current.

FIG. 3 is a chart illustrating solenoid current as a function of timecomparing one embodiment of the invention with a prior art.

FIG. 4 is a chart illustrating solenoid current as a function of timecomparing an embodiment of the invention with a prior art where the holdcurrent is reached before closure of the solenoid.

FIG. 5 is a second chart illustrating solenoid current as a function oftime comparing an embodiment of the invention with a prior art where thehold current is reached before closure of the solenoid.

FIG. 6 is a circuit schematic for a capacity charged circuit powering asolenoid according to one embodiment of the invention.

FIG. 7 is a second circuit schematic for a capacity charged circuitpowering a solenoid according to one embodiment of the invention.

FIG. 8 is an illustration of a closed loop determination process forregulating the change in the current in a solenoid as a function oftime.

Corresponding reference characters and designations generally indicatecorresponding parts throughout the drawings.

DETAILED DESCRIPTION

The present invention proposes a method and system for controlling afuel injection system equipped with a fuel injection solenoid. Morespecifically, the invention provides a method and system for reducingfuel injection timing errors associated with a fuel pump solenoid bydetecting a change in the closing point timing of the solenoid over aperiod of time. The time between the application of a voltage to thesolenoid and the instant at which the solenoid actually starts moving iscritical and is the Closing Point Detection (CPD) timing.

Referring to FIG. 1, one embodiment of a solenoid control system 100according to one aspect of the invention includes one or more processors102 executing computer-executable instructions 130. Processor 102 iselectrically coupled to memory 128. Memory 128 may store computerexecutable instructions 130 and may store one or more determinationsmade by the processor. Processor 102 is electrically coupled to asolenoid driver circuitry. Solenoid driver circuit 104 providesenergizing power (voltage and current) to a solenoid 112. Solenoiddriver circuit 104 includes sub-circuits including one or more of a highside driver circuit 136, a low side driver circuit 138, a high sidecurrent measurement circuit 140, a low side current measurement circuit142, and a capacitive charge circuit 144.

Processor 102 provides control signals to solenoid driver circuit 104including a high side command signal 106 indicating an on/off for thehigh side powering of the solenoid, a low side command signal 108indicating an on/off for the low side powering of the solenoid, and acapacitive charge circuit command signal 110 indicating and on/off forthe capacitive charge circuit. Processor 102 is also electricallycoupled to a linear voltage digital to analog converter (DAC) 118.Processor 102 provides a linear voltage signal 126 to the linear voltageDAC 118 that in turn provides the analog charge value signal 120 foreach channel or for each cylinder to solenoid driver circuit 104.

Solenoid driver circuit 104 provides the capacitive charge to solenoid112 in response to the analog charge value signal 120. The high sidecurrent measurement circuit of the solenoid driver circuit 104 providesa high side current measurement output 122 to an analog to digitalconverter 116. The low side current measurement circuit of the solenoiddriver circuit 104 provides a low side current measurement output 124 tothe analog to digital converter 116. The analog to digital converter 116provides the measured data to processor 102. Processor 102 and analog todigital converter 116 coordinate the determination of the channel orcylinder associated with the measurements and determinations.

Referring to FIG. 2, graph 200 illustrates solenoid current 202 as afunction of current value (y-axis) and time (x-axis). Current 202 is afunction of the voltage applied to solenoid 112 by solenoid drivercircuit 104. Associated in time with solenoid current graph 220 arecontrol signal timing diagrams 220, 240 and 260, for command signals.Signal timing diagram or graph 220 illustrates the timing for on (high)and off (low) digital signals for the low side electrical driver orpowering circuit for solenoid 112. Signal timing diagram 240 illustratesthe on and off signal positions as a function of time for the high sidecontrol signal for high side electric powering circuit for solenoid 112.Signal timing diagram 260 illustrates the on and off signal for thecapacitive charge circuit for solenoid 112. As illustrated, each ofgraphs in FIG. 2, graphs 200, 220, 240, and 260, have common timingwherein a point in time for each is the same point in time for each ofthe other timing graphs, for example time t₁. This group of graphsillustrates the interrelationship between the three control signals 106,108, and 110 and the current 202 through the solenoid as a function oftime.

At time t₀, current 202 is I₀ that may in some embodiment be anun-energized state of zero current. In other embodiments, current I₀ maybe an amount greater than zero. At time t₀, processor 102 initiates thesolenoid activation sequence which includes generating an on conditionin both high side control signal 106 and low side control signal 108 asindicated in timing diagrams 240 and 220, respectively. In response,solenoid driver circuit 104 applied high side powering and low sidepowering to solenoid 112 and the current increases from I₀ at time t₀ toI₁ at time t₀. At this point, solenoid driver circuit 104 measures thecurrents in solenoid 112 and provides these measurements to ADC 116 thatin turn provides them to processor 102. Processor 102 compares thecurrent 202 to a predetermined phase 1 maximum current level and whencurrent 202 reaches the predetermined phase 1 maximum current levelprovides an off low side driver signal 108 to solenoid driver circuit104. Phase 1 is shown as 204 that is the time interval between t₀ andt₄. Upon turning off the low side powering, current 202 decreases fromI₁ to I₂ at time t₂. Processor 102 provides an on/off control signal 108to the low side driver such that current 202 is maintained between amaximum value of I₁ and a minimum value of I₂, averaging at apredetermined pull-in current value of I₃.

Processor continues to pulse the low side driver for a defined period oftime and then at time t₃ turns off the low side driver as indicated bytiming signal 220 at time t₃. Upon turning off the pulsing of the lowside driver, current 202 through solenoid 112 decreasing as the storedenergy dissipates to ground. Processor 102 initiates an on controlsignal 110 for the capacitive charge circuit at time t₄. Time t₄ being apredefined period of time following t₃, which is referred to as ablanking window 218. Current 202 continues to decrease as a function ofthe capacitive charge circuit and other electrical characteristics ofsolenoid 112 and solenoid driver circuit 104. This decrease isillustrated as the decrease in current 202 at time t₄ of I₂ to the valueof I₄ at time t₅. The slope of the current line as a function of timefrom I₂ at t₄ to I₄ at t₅ being a function of the capacitive chargecircuit and the provided analog charge value 120. Processor 102determines the desired capacitive charge value 120 to regulate, control,or condition solenoid current 202 during this phase 2 (indicated by206). Processor 102 regulates the slope of current 202 as a function oftime between t₄ and t₅ such that the slope is within an upper bound 210and a lower bound 212.

In graph 200, time t₅ indicates the point in time when the core oractuator of solenoid 112 closes. Upon closing, current 202 increases dueto the change in the electrical characteristics of solenoid 112 as afunction of solenoid driver circuit 104 and specifically as a functionof the capacitive charge circuit. Processor 102 continues to measurecurrent 202 based on measurements of solenoid driver circuit 104 andfeedback on the high side current 122 and low side current 124 to ADC116. When processor 102 detects an increase of current 202 from aprevious value (shown as I₄) to a value I₅, the processor determinesthat solenoid 112 has closed. The determination of the closing ofsolenoid 112 may, in one embodiment, be based on a change of the currentas a function of time from a negative slope to a positive slope asindicated by the slope of line 220 from I₂ at t₄ to I₄ at t₅ and theslope of line 214 from I₄ at t₅ to I₅ at t₆. As illustrated, theprocessor requires a time period t₆-t₅ to determine the change incurrent 202 over time is indicative of a closing of solenoid 112.

Upon detection of the closing of solenoid 112, processor 102 provides anoff signal via the capacitive charge control signal 110 to the solenoiddriver circuit 104. The solenoid driver circuit 104 removes powering ofthe capacitive charge circuit as indicated at time t₆ on capacitivecharge signal 260. Processor 102 provides time t₆ or the determined timet₅ in fuel timing signal 132 to a fuel injection controller 134. Uponremoval of the capacitive charge powering of solenoid 112, current 202decreases from current I₅ at time t₆ to current I₆ at time t₇. Whenprocessor 102 determines that current 202 has reached predeterminedcurrent level I₆, processor 102 initiates an on signal via the low sidecontrol signal 110 so that low side driver provides powering to solenoid112. Processor 102 once again pulses low side driver between an on stateand an off state such as to maintain current 202 at between a maximumvalue of I₇ and a minimum value of I₆, with an average current of I₈. I₈is referred to as the holding current and this period of time isreferred to as the current hold phase or phase 3 (208). After apredetermined period of time, processor 102 terminates the pulsing ofthe low side driver powering and the high side powering as indicated attime t₉ as shown in graphs 220 and 240. In response to the terminationof both the high side powering and the low side powering, current 202decreases from value I₇ at time t₉ to I₀ at time t₁₀. This is referredto as phase 4 210.

When solenoid 112 is closed, fuel is provided by the fuel injectionsystem to the associated cylinder of the engine. This fuel-passingperiod begins with the actual opening of solenoid 112 and ends when thesolenoid opens (not shown) which is some point in time after t₉.

In operation, one aspect of the invention is a solenoid closing pointdetection (CPD) apparatus and method wherein CPD is time or degrees fromthe time of solenoid actuation to the time when solenoid 112 is closed.The solenoid closure results in a characteristic slope change in thecurrent 202. The computer instructions 130 of the processor 102determines when and how to condition the current slope change. Theaccuracy of the detection can be validated using a measurement systemfor solenoid movement and comparing it to the value computed insoftware.

As discussed above, solenoid current 202 has four phases as a functionof time. Phase 1 (204) is the pull-in current phase. At the beginning ofthis phase, the high side driver is turned on and kept on until thebeginning of phase 4 (injection end). During phase 1 (204), the low sidedriver provides low side powering until a specified pull-in currentlevel is attained I₁. After this, the pull-in current is regulated bypulsing the low side driver to average current value of I₃. The solenoidcurrent reaches peak current in a specified time t₁ that may be 850microseconds (μsec). The initial current slope during pull in phase canvary as a function of cable length, solenoid, and power supply voltage.The pull-in phase overcomes the damping and/or friction of thestationary solenoid 112. At the end of pull-in phase, low side driver isturned off.

Phase 2 (206) is the closing point detection phase during which acapacitive charge circuitry is enabled thereby providing capacitivecharging powering. The window between the time low side driver is turnedoff t₃, and time t₄ when capacitive charge circuitry is enabled iscalled blanking window 218. The capacitive charge value 120 used for thecharge circuitry is based on feedback calculation from previous firingof solenoid 112. The closing point of solenoid 112 is detected when thedecaying current slope goes from a steady negative to a positive value,as long as this occurs within a specified “CPD window.” The CPD windowmay be restricted to a predetermined period of time such as 600-700 μsecto avoid saturation of solenoid, current 202 dipping to or below thehold current minimum I₆ during this phase. At the instant the closing ofsolenoid 112 is detected or when the CPD window or predefined timeperiod expires, the capacitive charge circuitry is turned off and phase2 ends when the current reaches the minimum hold current level I₆. As aresult of solenoid closure, pressure increases in high-pressure fuelline causing a fuel injector needle to lift.

At the end of pull-in current phase, the low side solenoid driver isturned off, and then the current starts decaying down, at a ratedictated by impedance of the circuit (this varies as a function ofsolenoid, cable length, ambient conditions, power supply voltage). Thecapacitive charge circuit is enabled by a charge on/off digital signalprovided by the microcontroller for each channel that canreduce/increase the slope at which current decays during the CPD phase.The amount the slope is changed for a particular solenoid depends on theanalog charge value provided by the microcontroller through a linearvoltage digital to analog converter. Without this feature, it ispossible that the decay is so rapid where the hold current is reachedbefore solenoid closure occurred. The capacitive charge circuit iscontrolled by processor 102 such that the slope of current 202 as afunction of time can be varied within reasonable bounds 210 and 212. Inthe “linear” voltage mode, the transistor is “partially” open, thusresulting in slowing of the solenoid driver turn off. Processor 102executes instructions 130 that provide a closed loop algorithm tomanipulate the capacitive charge circuit to regulate the current slopeto a specific value, with dead zone on slope error, and saturation oncharge value. The slope estimation from the current measurement is doneby various methods for differentiation.

Phase 3 (208) is the current hold phase. During phase 3, solenoid 112 isheld in the closed position by holding current 202 at a specified holdcurrent level averaging I₈. Current 202 is held at the hold currentlevel I₈ by turning low side driver on and off. During phase 3 whilesolenoid 112 is held in the closed position, fuel is delivered to thecylinder.

Phase 4(210) is end of injection phase. During phase 4(210), current 202in solenoid 112 decreases from I₇ to I₀ or to zero causing solenoid 112to return to the open position. Low side and high side drivers areturned off to initiate the beginning of phase 4.

Referring now to FIG. 3, a similar graph as shown in FIG. 2 isillustrated. However, several of the aspects of the current inventionare shown in comparison to the prior art. As illustrated, after removalof the low side powering at time t₃, the prior art current 302 decreasesfrom I₂ at time t₄ to I₉ at time t₅′. t₅′ is the point in time whensolenoid actually closes. As shown, in the prior art when the solenoidcloses, current 302 changes slope as indicated by 304. However the slopeof 304 does provide an increase in the current and does not increase orchange from a negative slope to a positive slope. As such, in prior artsystems it is more difficult, costly, and takes a longer period ofdetection time for the system to accurately detect the change in current302 resulting in the closing of solenoid 112.

In another comparison, FIG. 4 illustrates a problem with the prior artthat is solved by one aspect of the invention. As shown, the prior artresults in a current 402 that decreases from I₂ at t₄ when the low sidepowering is removed to the I₆ at time t₇′. Processor 102 detects thecurrent value of I₆ and initiates pulsing of the low side driver betweenI₇ and I₆ to the current hold level of I₈. However, when current 402decreases to I₆ such that t₇′ occurs before that actual closing ofsolenoid 112, as illustrated as t₅, the prior art system cannot detect achange in current 402 that results from the closing of solenoid 112. Incontrast, when capacitive charge powering is turned on at time t₄,current 202 is conditioned by capacitive charge circuit to reduce thedecrease in current 202 over time such that current level I₆ is notreached until after the closing of solenoid 112 at time t₅.

FIG. 5 similarly illustrates that without the charge circuitconditioning of the solenoid, current 502 decreased from I₂ at t₄ to I₆at t₇′ prior to the closing of solenoid 112 at time t₅.

One embodiment of a solenoid driver circuit for CPD detection isillustrated in FIG. 6. In this circuit design, solenoid 112 is connectedon the high side to high side driver 602. High side driver 602 iscontrolled by high side control signal 106. High side driver 602 isconnected via a high side measurement resistor 604 to voltage source606. Voltage source 606 is illustrated as a +24 volt voltage source butmay be any voltage source. A high side current detector 608 iselectrically coupled to both the low side and high side of high sidemeasurement resistor 604 and provide a high side current 122 to analogto digital converter 116. The low side of solenoid 112 is electricallycoupled to a free wheel diode 612 that is also electrically coupled topower source 606. The low side of solenoid 112 is also electricallycoupled to a low side driver 610. Low side driver 610 is connected to aselection device 614 that specifies that mode of operation of the lowside driver 610. Selection device 614 includes four selection modes:Off; Freewheeling; Linear mode; and On. The low side driver is alsoelectrically coupled to a low side measurement resistor 620. Low sidemeasurement resistor is connected to a ground 624. A low side currentmeasurement device 622 is connected to both sides of low sidemeasurement resistor 620 and provide a low side current measurementsignal 124 to analog to digital converter 116.

Thus, in operation, the solenoid driver 600 as illustrated in FIG. 6 canbe operated in four modes. In the Off mode, solenoid 112 is in ade-energized state. Both a high side driver 602 and a low side driver610 are OFF and therefore no current flows in solenoid 112. TheFreewheeling mode is utilized during the negative current slope of thepull-in and the hold phases. High side driver 602 is ON and low sidedriver 610 is OFF. Current 202 flows from the power source 606 throughsolenoid 112 and back to power source 606 through a freewheel diode 612.In this mode, current 202 rapidly decays to zero. The linear mode isutilized during the CPD window. During this mode, high side driver 602is ON and low side driver 610 is partially ON or pulsed to provide apredetermined current 202 level. In this partially ON state, low sidedriver 610 is pulsed to maintain a predefined current. Current 202 flowsfrom power source 606 through solenoid 112 and low side driver 610 toground 624. Current 202 decays slowly until it is reduced to zero. Therate of decay depends on how much low side driver 610 is ON during thepartially ON pulsing phase. Processor 102 defines the amount ofpartially ON pulsing by measuring the rate of current decay during theCPD-window. Processor 102 adjusts the level of the linear voltage viathe D/A-converter 118.

Mode 4, the On Mode, is used during the positive current slope of thepull-in and the hold phase. Both high side driver 602 and low sidedriver 610 are ON. Current 202 flows from power source 606 throughsolenoid 112 and low side driver 610 to ground 624. Current 202increases rapidly during this mode.

Referring now to FIG. 7 is another circuit schematic for a capacitycharged circuit powering a solenoid according to one embodiment of theinvention. In this embodiment, solenoid 112 is connected to capacitor702, which is connected to ground 624. Solenoid 112 is also connected toa transistor 704 and to diode 612. Diode 612 is also connected to powersupply 606. Linear voltage 118 is connected to resistor 706, which isconnected to capacitor 708. Capacitor 708 is connected to resistor 710,which is also connected to transistor 704.

Referring to FIG. 8, an illustration of a closed loop determinationprocess as provided by the computer-executable instructions 130 ofprocessor 102. As discussed above, processor 102 executes computerinstructions 130 to determine the capacitive charge value 120 for thecapacitive charge circuit. In order to accomplish this, in oneembodiment as illustrated in FIG. 8 and the logic illustrated at 800,processor includes a reference slope 802 which may be stored in memory.The reference slop 802 is compared at block 804 to a previouslydetermined current slope. The current slope is compared to a dead zonein block 806, which determines a predetermined range of deviation forthe current decay or slope. In block 810, the slope error is determinedand the analog charge value is determined or specified as a function ofthe determined slope error. In block 812 a saturation is determined andthe saturation is provided to the charge and driver circuits in block814, which results in a particular solenoid current 202. The solenoidcurrent is measured and the solenoid current slope is estimated andprovided back for the next comparison to the reference slope. Such aprocess provides for a continuous and real-time comparison of the slopeof current 202 and the determination of the capacitive charge valuebased on the reference and most recent determined current slope.

In another embodiment of the invention, processor 102 determines aclosing point detection (CPD) slope signature by regulating current 202such that the current slope changes from a negative to a positive slopevalue in response to a closing of solenoid 112. Processor 102 detectsthe solenoid closing using an algorithm that places conditions on bothdi/dt and d₂i/dt₂ to be positive to determine the closing point. Assuch, any noise issues by dependence on d₂i/dt₂ alone are mitigated bythe distinctive signature of CPD (as a result of regulated slope withcapacitive charge circuitry), and conditioning CPD on di/dt itself. Thisis an improvement to operating detecting the closing point as a functionof d2i/dt2>0). Such a detection scheme is susceptible to noise oncurrent signal, which makes it difficult for the closing to be detectedfrom any noise. Additionally, the present invention is an improvementover simply determining a threshold as a function of d2i/dt2, i.e.,declare CPD only if d2i/dt2>threshold. In this case, such adetermination is difficult to reliably avoid incorrect detections and atthe same time, avoid missing detections.

In another embodiment of the invention, the closing point window 216 maybe adaptively determined as a function of real-time measurements andoperating characteristics or parameters of the fuel injection system orengine. In this invention, CPD window start is also a function ofsolenoid power supply voltage and optionally, cylinder position. Thismulti-dimensional function accounts for known variations of CPD withengine speed, cam position and cylinder position (including effect ofsolenoid cable lengths to various cylinders and bank). This function isoptimized by performing a design of experiments on locomotives withvariations of speed and timing for various cylinders. It is expectedthat other variations such as pump-to-pump and locomotive-to-locomotivestill keep CPD within the CPD window. This invention recommends aprocess for testing with these variations and ensuring that CPD isdetected within the CPD window. Beyond these, this invention employs anoptional scheme for adaptively varying the CPD window, to ensure morereliable CPD. In this embodiment, the CPD window is calibrated for eachlocomotive cylinder periodically, either in real time during operation,or at scheduled service intervals. In one embodiment, a CPD windowfunction is initialized per a default function of rpm, timing, solenoidvoltage and other known variations. CPD statistics such as a mean and astandard deviation are collected as a function of rpm, timing, etc., foreach cylinder, during normal locomotive operation, or per a special testduring manufacturing or maintenance service. The CPD window function foreach cylinder is adjusted within constraints, such that CPD statisticsfall within the CPD window, preferably in the center. The newly computedCPD window function is used for CPD window determination. The CPD windowis recalibrated from time to time, to account for aging, and locomotivecomponent changes.

This is an improvement over prior art system where the closing pointdetection window 216 start time, relative to the start of solenoidactivation, is a static function of engine speed and injection timingcommand. Such prior art restricts CPD window 216 to a value typicallyaround 500-700 μsec based on predetermined solenoid saturationmeasurements.

In another aspect of the invention, a closing point detection (CPD)value from one injection cycle is used for timing compensation for thenext injection cycle. Given the variation in operating conditions,variations between CPD are relatively small between two consecutivecycles, this leads to sufficiently accurate timing for emissions andfuel efficiency considerations. However, despite all the featuresmentioned above, CPD is not detected in certain cases, particularly,when Closing Point is not reached before end of injection. This happensfor negative duration angle commands, which may be needed for lightlyloaded conditions, or in response to reference speed or load changes. Ifsuch conditions persist for a while, CPD may not be detected for awhile. Under these conditions where CPD is not detected, a default CPDvalue is needed for use in timing compensation. Typically, the lastdetected CPD value from previous cycles is used as default value.

In contrast to prior art system, one embodiment of the current inventiondetermines a closing point deflection default value as a function of theoperating engine speed and timing at the time of the failure ofdetecting the closing point. When the same speed and timing conditionsexist, the CPD value is used as an exponentially weighted average of thepreviously detected CPD values. One such embodiment may be anexponentially weighted average of a sample size of 15 previouslydetected CPD values. When the conditions of speed and timing havechanged significantly since last detected CPD value, a default CPD forthe given cylinder is based on the most recent CPD average for theparticular operating speed and timing condition.

As can now be appreciated, the systems and methods herein describedprovide substantial advantages over the prior art. Such advantagesinclude improved accuracy and reliability in detecting the closing ofthe solenoid. Significantly, the system and method herein described mayalso be adapted for use with existing fuel injection systems andsolenoids.

When introducing elements of the present invention or preferredembodiments thereof, the articles “a”, “an”, “the”, and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including”, and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

Those skilled in the art will note that the order of execution orperformance of the methods illustrated and described herein is notessential, unless otherwise specified. That is, it is contemplated thataspects or steps of the methods may be performed in any order, unlessotherwise specified, and that the methods may include more or lessaspects or steps than those disclosed herein.

In view of the above, it will be seen that several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above exemplary constructionsand methods without departing from the scope of the invention, it isintended that all matter contained in the above description or shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense. It is further to be understood that the stepsdescribed herein are not to be construed as necessarily requiring theirperformance in the particular order discussed or illustrated. It is alsoto be understood that additional or alternative steps may be employedwith the present invention.

1. A system for detecting a closing point of a fuel injection pumpsolenoid associated with a cylinder of a locomotive diesel engine, thesystem comprising: a solenoid driver circuit for providing a current anda voltage to a winding of the solenoid, said solenoid having a low sidedriver and a high side driver; a sensor for detecting the currentthrough the winding of the solenoid; a detector responsive to the sensorfor detecting a change in a slope of the current as a function of time,said change of slope being from a decrease in current over time to anincrease in current over time; a processor responsive to the detectorand configured with computer instructions for determining a capacitivecharge value, said processor electrically coupled to the capacitivecharge circuit for providing the capacitive charge to the capacitivecharge circuit; and a capacitive charge circuit coupled to the solenoidfor modifying the voltage and the current provided by the solenoiddriver circuit as a function of the determined capacitive charge value.2. The system of claim 1, wherein the capacity charge circuitconditioning a current through the solenoid in response to a currentslope parameter, said current slope parameter defining a change in thecurrent after removal of an electrical charge to the solenoid.
 3. Asystem for detecting a closing of a solenoid, the system comprising: acurrent detector electrically coupled to the solenoid detecting acurrent through the solenoid; a processor responsive to the detector fordetermining a current slope characteristic, said current slopecharacteristic being a function of the detected current and time; acapacity charge circuit electrically coupled to the solenoid, saidcapacity charge circuit responsive to the determined current slopecharacteristic for conditioning the current through the solenoid toprovide for a change in the current slope characteristic after removalof an electrical charge in response to a current slope parameter.
 4. Thesystem of claim 1 wherein the current slope parameter is a function of acapacitive charge value determined from a generally contemporaneouslydetermined closing point detection.
 5. The system of claim 1 wherein thechange in the current slope characteristic after removal of anelectrical charge is a change in the current as a function of time froma negative current slope to a positive current slope.
 6. A method fordetecting a closing of a solenoid, the method comprising: detecting acurrent through the solenoid; determining a current slopecharacteristic, said current slope characteristic being a function ofthe current and time; and conditioning an electrical characteristic ofthe solenoid, said conditioning being responsive to a determined currentslope parameter, said current slope parameter defining a change in thecurrent after removal of an electrical charge to the solenoid.
 7. Amethod for detecting the closing point of a fuel injection pump solenoidassociated with a cylinder of a locomotive diesel engine, the methodcomprising: specifying a detection time period; conditioning anelectrical characteristic applied to the solenoid by applying acapacitive charge characteristic to the solenoid, said conditioningchanging the current as a function of time; detecting a current throughthe solenoid during the specified time period; determining a currentslope, said current slope being the incremental change in the current inrespect to time; detecting a change in the current slope from a negativecurrent slope to a positive current slope; and generating a signal inresponse to detecting the change in the slope.
 8. The method of claim 7wherein said detecting a change in the slope of the current as afunction of time is detecting a change in the slope from a negativeslope to a positive slope.
 9. The method of claim 7 wherein the currentis detected prior to an expiration of a detection time period.
 10. Themethod of claim 7 wherein said detection time period corresponds to aclosing point detection window, and wherein said closing point detectionwindow is determined as a function of solenoid power supply voltage. 11.The method of claim 10 wherein the closing point is detected when thedecaying current slope goes from a steady negative value to a positivevalue within a closing point window.
 12. The method of claim 10 whereinsaid closing point window is further determined as a function of acylinder position.
 13. The method of claim 10 wherein said closing pointwindow is further determined as a function of an engine operatingparameter.
 14. The method of claim 13 wherein said operating parameterbeing from the list: engine speed, cam position, cylinder position, andsolenoid cable length.
 15. The method of claim 13 wherein the engineoperating parameter is determined generally contemporaneous with thedetermining of the closing point window.
 16. The method of claim 10wherein said determining is a function of a previously determinedclosing point window.
 17. The method of claim 16 wherein determining aclosing point window is generally contemporaneous with the determiningof the previously determined closing point window.
 18. A system fordetecting a closing point of a fuel injection pump solenoid associatedwith a cylinder of a locomotive diesel engine, the system comprising: asolenoid driver circuit for providing a current and a voltage to awinding of the solenoid; a sensor for detecting the current through thewinding of the solenoid; and a processor responsive to the detectedcurrent and configured with computer instructions for specifying aclosing point window as a function of solenoid power supply voltage andfor detecting during the closing point window a change in the current asa function of time.
 19. The system of claim 18 further comprisingcomputer instructions for determining the closing point window as afunction of a cylinder position.
 20. The system of claim 18 furthercomprising computer instructions for determining the closing pointwindow is further determined as a function of an engine operatingparameter.
 21. The system of claim 20, wherein the engine operatingparameter is determined generally contemporaneous with the determiningof the closing point window.
 22. The system of claim 20 wherein saidoperating parameter being from the list: engine speed, cam position,cylinder position, and solenoid cable length.
 23. The system of claim18, further comprising computer instructions for determining the closingpoint window is further determined as a function of a previouslydetermined closing point window.
 24. The system of claim 23 wherein thedetermining a closing point window is generally contemporaneous with adetermining of the previously determined closing point window.
 25. Amethod for operating a fuel injection system of a locomotive dieselengine, the method comprising specifying a closing point detection valuefor a cylinder of the diesel engine in response to a failure to detectthe closing of the solenoid, said specified closing point detectionvalue being a function of an exponentially weighted average ofpreviously detected closing point detection values in response to aspeed and a timing of the diesel engine at the time of specifying beingcomparable to a speed and a of the diesel engine of the previouslydetected closing point detection values, said specified closing pointdetection value being a function of an average of generallycontemporaneously determined closing point values in response to thespeed and the timing of the diesel engine at the time of the specifyingvarying from a speed and a timing of the diesel engine associated with apreviously detected closing of the solenoid.
 26. A computer-readablemedium having computer-executable instructions for performing the methodof claim
 25. 27. A system for operating a fuel injection system of alocomotive diesel engine, the system comprising: a solenoid drivercircuit for providing a current and a voltage to a winding of thesolenoid; a sensor for detecting the current through the winding of thesolenoid; memory storing detected closing point detection values and aspeed and a timing associated with the detected closing point values;and a processor responsive to the detected current and configured withcomputer instructions for specifying a closing point value, saidcomputer instructions specifying a closing point detection value for acylinder of the diesel engine in response to a failure to detect theclosing of the solenoid, said specified closing point detection valuebeing a function of an exponentially weighted average of previouslydetected closing point detection values stored in the memory in responseto a speed and a timing of the diesel engine at the time of specifyingbeing comparable to a speed and a timing of the diesel engine of thepreviously detected closing point detection values, said specifiedclosing point detection value being a function of an average ofgenerally contemporaneously determined closing point values as stored inthe memory in response to the speed and the timing of the diesel engineat the time of the specifying varying a predetermined amount from aspeed and a timing of the diesel engine associated with a previouslydetected closing of the solenoid.